3) Your bestie says "I'm going to move to Manhattan and strip to pay my rent" and your response with a straight face, "Why not everyone else in the city does!" This then, of course, leads to hysterical laughter.

4) Something weird happens in the middle of a convo and you BOTH simultaneously; stop, stare in the direction of the weirdness with your mouths open, then look at each other, and die of hysteria all what asking "W.T.F" !!!

5) When they can say "my nipple hurts" feeling completely comfortable and looking at your face and just laughing.

6) When all you do is laugh until you cry and make blogs about it because there is no other person or group of people you would rather spend any amount of time with!!!

Those are just a few ways lol! How else can you tell? I would love to know!